The subject matter of this disclosure is generally related to fabrication of an integrated computational element (ICE) used in optical analysis tools for analyzing a substance of interest, for example, crude petroleum, gas, water, or other wellbore fluids. For instance, the disclosed ICE fabrication uses a support for formed layers of ICEs, where the support is shaped and arranged relative to a deposition source used to form the layers such that a shape of the support corresponds to a spatial profile of a deposition plume provided by the deposition source.
Information about a substance can be derived through the interaction of light with that substance. The interaction changes characteristics of the light, for instance the frequency (and corresponding wavelength), intensity, polarization, and/or direction (e.g., through scattering, absorption, reflection or refraction). Chemical, thermal, physical, mechanical, optical or various other characteristics of the substance can be determined based on the changes in the characteristics of the light interacting with the substance. As such, in certain applications, one or more characteristics of crude petroleum, gas, water, or other wellbore fluids can be derived in-situ, e.g., downhole at well sites, as a result of the interaction between these substances and light.
Integrated computational elements (ICEs) enable the measurement of various chemical or physical characteristics through the use of regression techniques. An ICE selectively weights, when operated as part of optical analysis tools, light modified by a sample in at least a portion of a wavelength range such that the weightings are related to one or more characteristics of the sample. An ICE can be an optical substrate with multiple stacked dielectric layers (e.g., from about 2 to about 50 layers), each having a different complex refractive index from its adjacent layers. The specific number of layers, N, the optical properties (e.g. real and imaginary components of complex indices of refraction) of the layers, the optical properties of the substrate, and the physical thickness of each of the layers that compose the ICE are selected so that the light processed by the ICE is related to one or more characteristics of the sample. Because ICEs extract information from the light modified by a sample passively, they can be incorporated in low cost and rugged optical analysis tools. Hence, ICE-based downhole optical analysis tools can provide a relatively low cost, rugged and accurate system for monitoring quality of wellbore fluids, for instance.
Errors in fabrication of the constituent layers of an ICE can degrade the ICE's target performance. In most cases, deviations of <0.1% and even 0.01% or 0.0001% from point by point design values of the complex indices of refraction, and/or thicknesses of the formed layers of the ICE can substantially degrade the ICE's performance, in some cases to such an extent, that the ICE becomes operationally useless. Those familiar or currently practicing in the art will readily appreciate that the ultra-high accuracies required by ICE designs challenge the state of the art in thin film deposition techniques. Conventionally, a support (sometimes referred to as a platen) that supports ICEs within the field of view of a deposition source is spaced apart therefrom and has a flat shape. Moreover, a size of the deposition source is typically smaller than a size of the flat support. In such cases, when an azimuthal axis of the deposition source intersects the center of the flat support, non-uniformities of deposition rates across the flat support are induced because a distance from the deposition source to ICEs supported near the center of the flat support is shorter than a distance from the deposition source to the ICEs supported near the edge of the flat support, and, thus more material is deposited per unit time at the center than at the edge.
Like reference symbols in the various drawings indicate like elements.